1. Field of the Invention
The present invention relates to a chainwheel, and more particularly to a chainwheel for multi-size crank modules.
2. Description of Related Art
A transmission system of a bike provides a power for moving the bike. The transmission system comprises a chainwheel, a crank module, a chain, and a rear sprocket. The crank module is combined with the chainwheel. The chainwheel is connected with the rear sprocket by the chain. In use, a user treads the crank module to rotate the chainwheel, and the rear sprocket is driven to rotate by the chain. Then, a rear wheel of the bike is driven to rotate by the rear sprocket, such that the bike can move forwards.
With reference to FIG. 5 and FIG. 6, a conventional chainwheel comprises a chainwheel body 70, multiple chain teeth 80, and five combining holes 90. The chainwheel body 70 is round and has a center point and a periphery. The chain teeth 80 are arranged along the periphery of the chainwheel body 70. The combining holes 90 are formed through the chainwheel body 70 and disposed equidistantly from one another. A hole distance R4 is defined between a center point of each combining hole 90 and the center point of the chainwheel body 70. The hole distances R4 between the center points of the combining holes 90 and the center point of the chainwheel body 70 are equal. A crank module C is combined with the chainwheel body 70 via the combining holes 90.
However, the conventional chainwheel can only be combined with the crank module of a single size. The manufacturer has to manufacture chainwheels of different sizes to fit the crank modules of different sizes. Therefore, the manufacture cost of the conventional chainwheels is increased.